Line Of Duty: A 'mugging off', a real life hint from Buckells back in 2017 and the bad spelling... the clues that have DEFINATELY told us the identity of The Fourth Man all along It was revealed during Sunday night's eagerly-anticipated finale that The Fourth Man - also known as H - was Superintendent Buckells Initially portrayed as a hapless character, it was revealed that he was in fact the criminal mastermind who had formed the secret network of bent coppers Many clues appear to have come to light since the show hit screens in 2012, including a real life note from actor Nigel Boyle, who tipped off fans in 2017